The inner surface of pneumatic rubber tires is typically comprised of an elastomeric composition designed to prevent or retard the permeation of air and moisture into the carcass from the tire's inner air chamber. It is often referred to as an innerliner. Innerliners have also been used for many years in tubeless pneumatic vehicle tires to retard or prevent the escape of air used to inflate the tire, thereby maintaining tire pressure. Rubbers which are relatively impermeable to air are often used as a major portion of said innerliners and can include butyl rubber and halobutyl rubbers. U.S. Pat. No. 3,808,177 discloses other polymers which may also be relatively impermeable. It is known that acrylonitrile/butadiene copolymers can be relatively impermeable.
The innerliner is normally prepared by conventional calendering or milling techniques to form a strip of uncured compounded rubber of an appropriate width, which is sometimes referred to as a gum strip. Typically, the gum strip is the first element of the tire to be applied to a tire building drum, over and around which the remainder of the tire is built. When the tire is cured, such innerliner becomes an integral, co-cured, part of the tire. Tire innerliners and methods of preparation are well known to those having skill in such art.
The preparation of a gum strip composed entirely of compounded chlorobutyl or bromobutyl rubber has been observed to have some processing and fabrication problems such as sticking to processing equipment during the milling and calendering operations.
Furthermore, it has sometimes been desired to provide a gum strip composition for the innerliner which has suitable processing properties, building tack in its uncured state and cured adhesion to the tire carcass while also having a satisfactory degree of air impermeability.